let s: string | number = "1"
let a: string = "1"

interface Person {
    name: string
    age?: number
    [propName: string]: string | number
}

let tom: Person = {
    name: "tom",
    a: "a",
    b: "a"
}

let ob = { "a": 1 }
// ob = {} 报错
// ob = 1 报错
ob = { "a": 2 }

// 任意类型, 联合类型 ....

s = 1
console.log(a)